Stevens is an unlikely liberal icon. When he was appointed, he told me recently, he thought of himself as a Republican and always had—“ever since my father voted for Coolidge and Harding.” He declined to say whether he still does. For many decades, there have been moderate Republicans on the Court—John M. Harlan II and Potter Stewart (appointed by Eisenhower), Lewis F. Powell and Harry Blackmun (Nixon), David H. Souter (Bush I). Stevens is the last of them, and his departure will mark a cultural milestone. The moderate-Republican tradition that he came out of “goes way back,” Stevens said. “But things have changed.” […]

Still, Stevens’s views suggest a sensibility more than a philosophy. Many great judicial legacies have a deep theoretical foundation—Oliver Wendell Holmes’s skeptical pragmatism, William J. Brennan’s aggressive liberalism, Scalia’s insistent originalism. Stevens’s lack of one raises questions about the durability of his influence on the Court.

But, more than anything, his career shows how the Court has become a partisan battlefield. In that spirit, Roberts last week denounced President Obama’s criticism of the Court in his State of the Union address, saying that the occasion had “degenerated to a political pep rally.” When Stevens leaves, the Supreme Court will be just another place where Democrats and Republicans fight. […]

After his clerkship, Stevens returned to Chicago and took a job at one of the city’s first religiously integrated law firms. Abner Mikva clerked on the Supreme Court the year after Stevens, then returned to Chicago to start a career in public life. “Those were the days when there was such a thing as a moderate Republican, and that’s what he was,” Mikva said of Stevens. “He was a pretty conservative Republican on economic issues, but he was always a great progressive on civil rights and social rights.” […]

Stevens, throughout his years on the Court, has drawn not just on history and precedent but on contemporary values and even on his own experience as a judge. According to Stevens, that approach has its origins in his brief stint as a lawyer on the staff of the House Judiciary Committee. “That was probably one of the most important parts of my education,” Stevens told me. He recalled an incident involving an antitrust law: “I remember explaining one of the tricky problems in the statute to one of the members of the committee. I got all through it, and he said, ‘Well, you know, let’s let the judges figure that one out.’ ”

What that told him was that “the legislature really works with the judges—contrary to the suggestion that the statute is a statute all by itself,” Stevens said. “There is an understanding that there are areas of interpretation that are going to have to be filled in later on, and the legislators rely on that. It’s part of the whole process. And you realize that they’re not totally separate branches of government—they’re working together.”